1. Field of the Invention
This invention relates in general to antennas and more particularly, to a dual-frequency-band/dual-element, single connector antenna with an embedded diplexer.
2. Description of the Related Art
Wireless communication is accomplished through use of a radio connected to an antenna. An antenna is an impedance-matching device used to absorb or radiate electromagnetic waves into the atmosphere. The function of the antenna is to “match” the impedance of the propagating medium, which is usually air or free space, to the source of the radio waves, i.e., output of the radio.
Antennas are available in many different shapes and sizes. The particular shape and size of an antenna designed for a particular application depends on many factors, such as the frequency or range of frequencies being received and transmitted, the expected environment the antenna will endure, size limitations of the structure the antenna is to be installed upon, power efficiency limitations, impedance limitations, application particulars, and many more.
Additionally, a common use of antennas is on ground or airborne vehicles. An antenna can be placed on various locations on the body of the vehicle, providing communication between the vehicle and other radio-wave-receiving entities, such as handhelds, base stations, other vehicles, and more. The communication links include ground to air, air to air, or ground to ground. All vehicles, whether airborne or terrestrial, have a finite amount of surface area in which antennas can be placed. It is therefore a common design goal to provide as efficient an antenna as possible in the smallest package possible.
Antennas that are installed on the exterior of vehicles must withstand heavy torque from wind and debris, resist moisture, withstand extreme and rapid temperature changes, heavy vibrations, and other environmental hazards. For this reason, antenna “assemblies” are utilized with includes a shell, which covers and protects the radiating portion of the antenna assembly, called the “element”. The shell must be rugged and strong. Antenna shells are often constructed of fiberglass or other composite materials. Composite materials are chosen as a housing for the elements because they are lightweight, structurally robust, and allow radio waves to pass without appreciable attenuation.
The single largest dictator of the physical size of an antenna element is its intended frequency range. An antenna of a given size has an optimum frequency with which it is most efficient. Acceptable efficiency can also be realized with frequencies that vary above and below the optimum frequency, to a certain degree. For efficiency to remain at an acceptable level, the element should increase in length as the frequencies decrease. Likewise, the element should decrease in length as the frequencies increase.
In many applications, it is necessary to broadcast or receive over a relatively broad range of frequencies. As discussed in the preceding paragraph, an element of a fixed length is efficient at a single frequency, with performance dropping as the frequency varies from that single frequency. Transmitting or receiving a broad frequency range on a single element will result in poor performance and wasted power.
One Prior Art solution for transmitting and receiving one or more distinct broad ranges of frequencies has been to utilize two or more separate antennas (with separate housings), each for a specific range of frequencies, and each with a separate connector to the radio. However, mounting multiple antennas on a surface requires dedicated space for each antenna footprint. As mentioned above, antenna mounting space on vehicles is finite. Therefore, utilizing multiple antennas is disadvantageous in terms of space consumption.
Additionally, when one antenna is in close proximity, and in the beam field of another, transmits a signal, that signal will be received by the other antenna and fed back to the radio. This effect can damage the transmitting radio and is undesirable. To prevent or reduce the effects of poor frequency isolation between the antennas, a filter is used to isolate the intended frequency range of each antenna and reject frequencies outside that range. Some prior art designs provide filters in-line with the coaxial cable while other filters are integrated inside the antenna housing. Providing separate antennas with separate filters and connectors adds extra expense and additional potential failure points to the design.
Other Prior Art designs have put multiple elements of varying size inside a single antenna housing. Multiple elements in a single antenna assembly can result in a significant space saving over two separate antennas. However, elements in the same housing are in very close proximity. The small distance between the elements may cause them, as described above, to suffer from isolation problems, thereby necessitating the presence of one or more filters. Prior art antennas of this type utilize separate connectors for each element with in-line filters providing the necessary isolation between the frequency bands.
Multiple connectors on a single antenna is a disadvantage. This is because it requires a radio with multiple cables and connecters. In many vehicular applications, access to inside the area of the body where the antenna is to be installed is limited. The installation step of connecting both connectors is difficult and time consuming. Additionally, the multiple connectors creates added cost for the extra parts, added time, and cost for testing procedures, increased failure points, and many other disadvantages.
Accordingly, a need exists to overcome the shortcomings with the prior art and to provide a dual-band/dual-element antenna with a single connector that also provides adequate isolation between frequency bands.